Tunneling, α2F(ω), and transport in superconductors: Nb, V, VN, Ba1−xKxBiO3, and Nd1.85Ce0.15CuO4

Abstract

The electron-phonon contribution to the normal-state resistivity, ρ(T), has been calculated for the following conventional and oxide superconductors: Nb, V, VN, Ba1−xKxBiO3, and Nd1.85Ce0.15CuO4 (NCCO). The resistivity formula developed from the Boltzmann equation by Ziman and Allen is used, incorporating measured physical constants. The calculations are novel in that they incorporate the electron-phonon spectral function, α2F(ω), for each material as obtained from superconducting tunneling measurements, the same function that yields the superconducting transition temperature Tc. New tunneling and transport data are presented for VN. Fits to the experimental ρ(T) are obtained over a wide temperature range with only two parameters: the plasma frequency ωp, which is in good agreement with independent measurements and a saturation resistivity, ρs, which manifests itself at high temperatures. We find that the T-dependent normal state ρ(T) is completely accounted for by phonon scattering in all materials except NCCO, where an additional electron-electron scattering term appears to be present. Apart from developing a consistent description of superconductivity and normal-state transport, several important issues are raised by the present work including indications of a conventional Fermi-liquid normal state in NCCO, insight into the importance of the shape of the Fermi surface in determining ρ(T), and the role of high-energy optical phonons in oxide and nitride superconductors.

Source-reported materials — not catalogue approval

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